backend and frontend now reference their own images (BACKEND_IMAGE_PATH/TAG,
FRONTEND_IMAGE_PATH/TAG) instead of the shared emi/thermograph/app. deploy.sh
takes SERVICE=backend|frontend|all, rolls just that service with --no-deps,
persists each service's live tag in deploy/.image-tags.env so a single-service
deploy never disturbs the sibling, and fixes the old IMAGE_TAG:? guard that
made every workflow deploy hard-fail. Health-checks per service (8137/8080).
Claude-Session: https://claude.ai/code/session_01RdARHDJaYC1wSQRTYM6t3Z
ce454e0be6